Electrical switch-contact.



F. R. MoBERTY. ELECTRICAL SWITCH CONTACT.

APPLICATION FILE-11111127, 1908.

1,046,823. I I I Patented Dec. 10, 1912.

if if Inventof:

To all whom it may concern:

FRANK R. MOBERTY, OF NEW BQGHELLE, NEW-YORK, ASSIGNOIB. T0 WESTERN ELECTRIC COMPANY, OF CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIS.

ELECTRICAL swr'rcn-con'mcr.

Be-it known that I, FRANK MOBERTY, a citizenof the UnitedStates, residing in the town of New Rochelle, county of VVest- Chester, and State of New York, have invent-ed a new and useful Improvement in Electrical Switch-Contacts, of which the following is a full, clear, concise, and exact description.

My invention relates to the.construction of electrical switch contacts, particularly for telephone apparatus, in which the contact surfaces are composed of a material'difi'erent from that of the switch levers. In other applications of even date herewith, I have described a material for the contact faces of such electrical switches, said material consisting of a thin platinum foilbacked by a heavy plate of pure copper electrolytically deposited on the foil. I have also described therein'a process for making and mounting the-contacts or contact faces. My invention herein described relates t the construction of contact points, disks or plates from said material and their combination with the-sWitch-parts, such as switch springs, of telephonic apparatus.

In, the manufacture of telephonic appliances, it is necessary to provide a single form of contact capable of meeting a variety of conditions arising at the switch contacts with respect to current, inductance, me chanical' 'w'ear and pressure. This invention is the result of a study of such electrical and mechanical conditions, from which study, the following facts werd developed: During the cycle of closing and breaking the circuit, six different. stages of electrical action are distinguished. Duringthe firststage, a spark breaks across between the ap proaching contacts. In the second sta e,

. the discharge becomes a glow. In the thlrd stage the metals are'brought into contact and ,heat is developed due to .the resistance of the metal. The fourth stage covers the period during which-the metals are pressed together to produce a circuit of low resistance. During the separation of the contacts the fifth stage is established, in which an arc of increasing resistance is'formed, which.

.when ruptured gives place to the' sixthstage, 3 the open circuit. In non-lnductlve circuits havingconsiderable voltage, the initial spark .(first stage). may be strong-and destructive Specification ofLetters Patent.

Patented Dec.1 0,1912.

Application filed February 27, 1908. Serial No. 418,129.

-metal. In inductive circuits, the spark is relatively feeble 'or'may be absent. In the m S M NT OFFICE-i Y by preceding discharges; these globules heat, by reason of the resistance of the metal, and tend to weld together. The dimensions of the welded area depend upon the heat developed and the fusibility of the metal.

Under continued pressure, the-stage of solid contact is reached. \Vhen the contact area In circuits having fairly high 1 In circuits carrying large current, whatever the voltage'inay be, the conditions produced during the third, Y

fects during the first, second and third stages fourth and fifth stages are destructive of the contacts. In non-inductive circuits, the efare strongly marked, while those in the. fifth stage are relatively feeble; but on the other hand, in inductive circuits, the destructive effects during the firstand second stages are relatively slight, while that taking place during the fifth stage is highly destructive.

The actions of thecurrents on the'metal under the different conditions of practice. may be enumerated as follows: tearing out of particles; evaporating the metal from either cathode or anode; heating the surface filaments of the metal, with dissipation or oxidation;- welding the contact surfaces breaking the welded joint with transfer of metal from one to the other; great heating of the anode crater, with transfer of the metal to the. cathode. I

The evaporatedmetal, if oxidizable, will 55 of the contacts, carrying ofi particles of the be oxidized and deposited'gin the neighborhood of the hot parts, the position depending upon the distribution of temperature in the parts and the temperature of condensation of the metal or oxid. In the case of those metals which condense at high temperatures and oxidize, the oigid may be deposited so near the contact surfaces as to interfere with subsequent operation. In the case of metals which evaporate and condense at relatively low temperatures, the loss of metal by evaporation and the welding will prevent the satisfactory operation. of the contacts. I Of telephonic appliances, such as line relays, for example, the great majority will be used a limited number of times during their lives, but a small number will "be subjected to very much greater usage and wear; so that the pitting or destruction of ""COI1taCtS may be slight in a great number of cases of any kind of appliances, but may be great in relatively a few cases. For this reason, it is desirable in practice that the great majorityof cases shall be met in a wholly satisfactory manner while the few cases shall be met in some way which shall avoid failure. The electrical contacts of this invention fulfil all of the conditions above .stated. v In the drawing accompanying this appllcation, Figure 1 represents a disk or plate of the material suitable for forming a plate contact. Fig. 2 shows a conical plate, disk or piece intended to form a point contact. 5 Fig. 3 shows in section a switch spring with the disk in place. Fig. 4 illustrates the combined spring and disk in final form. Fig. 5 illustrates the final form of contact point.

Fig. 6 shows a section of a pair of typical springs provided with contact disks of Figs.

land 2. Fig. 7 is a view, partly in section, of a contact screw carrying a tip of my im-' proved material. Fig.- 8 is a longitudinal section of a contact spring having a platinum face on each side. i The disks or plates of the material are struck out in a press in a concavo-convex shape. The disk for the plate (Fig. 1) may be one tenth inch in diameter; that for the point (Fig. 2) maybe eight hundredths inch in diameter. Each disk is composed of a face, a,-of platinum foil, which may be one thousandth inch thick, and a backing or base, I), of pure copper, electrolyticall deposited on the foil, which may be one fi tieth inch thick. These disks are formed by I a suit-able tool into cups, as shown in Figs. 1, 2,. and 3. As illustrated, the forming of the disks has been simultaneous with the punching. operation. Forcing these disks 4 mtothe concavo convex form makes the edges of. the disks conical. .These disks, 0 and d, are dropped into holes very slightly larger than the disks in'the switch springs ,65 or supporting parts, e and 1, respectively,

'ing the disk in place.

and then are struck by a tool which reduces the convexity of the cups and thereby spreads the metal in the holes as shown in Fig. 4. The peripheral edge of each disk is forced into binding engagement with the edge'wall of its perforation, thereby secur- It is preferable that the plate contact should be raised a little above the flush surface of the switch spring. Thepoint contact should protrude considerably from the spring.

The contact screw shown in Fig. 7 has an opening in the form of a cu p-shaped recess, 9, in its end, in which the conical contact point 9 like that shown in Fig. 2 is placed. Then, as before, the piece 7 is crushed down and spread in the recess, by means of a riveting tool.

In the spring, h, shown in Fig. 8 two diskcontacts, h" and 71,2, have been placed back to back in the hole h in the spring, and flattened into place.

The platinum faced contacts thus produced are held strongly in place with respect to mechanical forces, and also have an intimate and permanent electrical contact with the metal of the supporting parts. I

The process of forming the contacts requires great malleability of the metal as well as strong adhesion between the platinum and the copper. To meet this requirement the rotary process should be employed in electrolytically depositing the copper on the platinum foil, the latter being wrapped around a cylindrical mandrel rotating in the plating solution at a fairly high rate-say one thousand revolutions perminute; and

the platinum having been chemically cleaned in advance, the plating current is raised carefully from an extremely low value to a maximum. By this process, a very tough and strongly adherent plating a of copper is produced upon the foil.

Switch contacts of the present invention have in the great majority of cases, all the advantages of solid platinum contacts, and in addition, are of low cost. There'would be no great saving of cost if the platinum were made of such thickness as to meet the extreme wear of all appliances. The peculiar advantages of the use of the pure copper plating arise in the minority of cases in which the .electrical actions wear through the thin platinum facing. As an example, a platinum facing one thousandth inch thick will withstand the action of the ordinary current in the subscribers line for morethan 100,000 operations, which number exceeds the average number occurring in a life of say twenty years; but theplatinumof the contact would be perforated in cases of lines calling as frequently as 100 times per day fora periodof years. But the percentage of lines calling with such frequency is small.

, When the platinum is perforated the evapyoration of the copper extremely .s

slight copper being one ,of those meta which evaporates slowly under electrical action.

When contact with the first particles occurs (third stage) the low resistance of copper permits the minimum of heat; and, because of this fact and the relatively high melting point of copper, the melted globules fused together are small. When solid contact 00- curs, the copper does not weld strongly. For these reasons a slight force, such as is available in relays, is sufficient to separate thecontacts. During the arc (fifth stage) the copper is not volatilized in large volume,

for the reasons before noted, and it condenses mainly as clean metal upon'nearby parts. As a result ofthese characteristicsof the copper, and the method of attachin it,

I find that the contacts can'be success ull operated several hundred thousand times a ter perforation of the platinum in circuits carrying currentscapable of producing such perforationLxln circuits carrying currents of such feebleness as not to wear through the platinum, such as telephonic currents, the latinum alone serves.

I brass, tin, lead or zinc be used as backing, these metals give off large volume of OXldiZGd vapor as soon as perforation of the platinum 7 occurs "and revent subsequent closing of the circuit. ronused as abacking rusts and keeps the circuit open' after L perforation occurs. Nickel gives ofir vapor which condensing near the contacts, oxidizes with a thin but hard non-conducting film,

which after a few operations, prevents clos ing of the circuit.-

Attem ts have 'metals; vbut so far as I an' -aware, only. 'excessively thin films of platinum can be probeen made to provide t'act sur aces ofplatinum plated upon base 40 duced which fail to withstand either 'the meproperties of. the solder more than of the platinum and is re'adily'destroyed.

An electrical contact composed of 1atinum foil havin a backing of other metal electrolytically epositedthereoni I FRANK MOBEBTY.

. 7 Witnesses:

- Niorroms E. KERNA'N,

=W1LLIAM' G;. MoKNren r 

